The present invention concerns a method for operating a restraint system networked via a bus line in conjunction with a defective power supply, in which a central control unit and a plurality of data processing units are connected to the bus line, each of the data processing units being intended to drive one or more restraint devices, and the power for the data processing units being supplied from the central control unit.
The capabilities of vehicle restraint systems will increase substantially in the future in order to afford passengers still greater protection. This means that there will be a tremendous increase in the number of restraint devices and associated triggering means installed in vehicles. Examples of such restraint devices are driver and front-passenger airbags, which can optionally be activated in multiple stages, driver and front-passenger knee bags, side airbags for the driver and the front-seat and back-seat passengers, such side airbags optionally being provided for both the head and chest areas, seat-belt pretensioners, which also can be activated in multiple stages, optionally also roll bars, etc. A complex protection system composed of multiple restraint devices for each passenger will thus be installed in vehicles.
In the Conference Proceedings of the SAE International Congress and Exposition, Feb. 24-27, 1997, Detroit, a complex restraint system is described in the paper xe2x80x9cBus System for Networking Actuators for Restraint Systems,xe2x80x9d by J. Bauer, G. Mehler and W. Nitschke. By introducing a bus system that networks all the restraint devices to one other, the authors were able to eliminate the need for bulky cable harnesses. In this known system each restraint device has its own data processing unit, basically composed of a processor, data input and output circuits, a memory unit, a time and clock base and a power supply. This data processing unit, also referred to as a peripheral intelligent firing stage, is located in the immediate vicinity of the triggering means for the restraint device concerned, i.e., in a squib connector or on a substrate of the squib itself.
Each data processing unit receives its power from a central control unit via a bus line. The central control unit further determines which restraint devices are to be triggered, basing its decision on multiple sensor signals, for example from acceleration sensors, pre-crash sensors, seat occupancy sensors. To accomplish this, the central control unit addresses the data processing units concerned by means of a protocol transmitted via the bus line. Diagnostic test requests also go out from the central control unit via the bus line to the individual data processing units, which in turn send their diagnostic test responses back to the central control unit via the bus.
One essential requirement for a vehicle restraint system is that it remain operational to the greatest possible extent, even when circuit defects occur in the central control unit or the data processing equipment. Such a defect would be, for example, failure or defective operation of the power supply in the central control unit. An object of the present invention is, therefore, to advance a method by which the restraint system can be kept operational for potential triggering even when the power supply is defective.
This object is achieved in that if a defect occurs in the power supply present in the central control unit itself, a changeover is effected to the vehicle battery voltage as the new supply voltage, the central control unit then signals the changeover to the new supply voltage to all the data processing units via the bus line, and the data processing units thereupon adjust their circuits to the new supply-voltage level. These measures ensure that all the restraint devices in the vehicle can still be triggered reliably even if the restraint system""s own power supply should fail.
A comparator present in each data processing unit and designed to detect a short circuit on the bus line is switched over to a reference voltage that corresponds to the new supply voltage.
Once the data processing units have adjusted to the new supply voltage, the central control unit sends the data processing units no further information signals or control signals other than trigger commands. This ensures that trigger commands from the central control unit will be able to reach the restraint devices unimpeded.